The present invention is directed to a bicycle display device that displays various types of data such as the bicycle velocity and distance traveled, wherein the tire circumference can be simply, accurately, and reliably input.
Display devices for displaying various types of bicycle-related data, such as the bicycle velocity, distance traveled, and shift position of the shifter, are commonly mounted on bicycles. Of such data, the bicycle velocity and the distance traveled are important. Because a sensor monitors the wheel rotation, knowledge of the tire circumference is essential for displaying the bicycle velocity and the distance traveled. Thus, when a display device is attached to a bicycle, the circumference of the bicycle tires must be set up in the display device as an initial setting. Methods for establishing the tire circumference include inputting the tire outside diameter to calculate the nominal value for the tire circumference based on the outside diameter, or measuring the tire outer periphery and directly inputting the actual measured value.
Unfortunately, it is not possible to cover all types of operating conditions of the tire when calculating the nominal value for the circumference of the tire by inputting the outside diameter of the tire. For example, when the rider is mounted on the bicycle, the tire circumference deviates from the nominal value depending on the tire air pressure, the body weight of the rider, and the type of tire. That is because the tire is deformed by the body weight of the rider, and the extent of deformation is related to a variety of parameters, such as the tire outside diameter, width, structure, and type of rubber, thus making it impossible to ensure accurate measurement of the extent of deformation using just the outside diameter of the tire. The tire circumference thus cannot be accurately set merely by inputting the outside diameter of the tire.
When the tire circumference is measured while the rider is mounted on the bicycle, the accurate measurement of the tire circumference is complicated and cannot be readily managed by the rider. Differences in the set values also occur, despite deliberate attempts to make accurate measurements, because of deviation in the tire air pressure from that at the time of measurement, differences in the body weight of riders, and so forth.